1. Field of the Invention
This invention relates to a process for producing a thermosetting isocyanurate resin, and more particularly, to a process for producing a flame retardant isocyanurate resin by the polymerization of a polyfunctional isocyanate compound.
2. Description of the Prior Art
It has been known heretofore that organic isocyanates are liable to polymerize. Linear polymers of polyfunctional isocyanate compounds are commercially useful products, and such polymers having isocyanato groups are widely used as an intermediate for polyurethane.
Various processes for producing isocyanurate resins by polymerizing polyfunctional isocyanate compounds were tried. The resulting isocyanurate resins obtained from a polyfunctional isocyanate compound alone are self-extinguishing, but not stable at an elevated temperature so that the resins are not yet of commercial usefulness.
Japanese Patent Application Laid Open No. 49-94798 discloses a process for producing a thermosetting resin having isocyanurate rings and oxazolidone rings by reacting one equivalent of a polyfunctional epoxy compound with 1.5 - 5 equivalents of a polyfunctional isocyanate compound. Japanese Patent Application Laid Open No. 50-63100 discloses the use of a thermosetting resin having isocyanurate rings and oxazolidone rings as an electric insulating material. In these prior art patents the polymerization requires a long time to become complete and the resulting resin has a low flame retardancy.